Download Chapter 14: Human Heredity Thomas Hunt Morgan: studied

Chapter 14: Human Heredity
Thomas Hunt Morgan: studied genetics of fruit flies. Fruit flies are easier to
study then humans, they have 8 chromosomes, reproduced quickly, etc
In humans: 46 chromosomes (2 sets: 23 from Mom, 23 from Dad)
o Chromosome pairs are numbered 1-23, largest to smallest
o 22 pairs of homologous chromosomes (similar shape/size)
o Autosomes: first 22 pairs of homologous chromosomes (not sex
chromosomes)
o Sex chromosomes: last pair of chromosomes (23rd pair)
X Y (male) or XX (female)
Have 50% chance of getting XY, 50% chance of XX
Karyotype: picture of chromosomes usually taken during metaphase of
mitosis because best time to see them coiled up
Tetrad: Pair of homologues chromosomes side by side. 4 chromatids.
During Meiosis I these tetrads (homologous pairs) split
Pedigree: diagram showing inheritance of a trait through generations. Can
use them to determine if a trait is dominant, recessive, autosomal, sex-linked.
Sex-linked Trait: a trait carried on the X sex chromosome. Because males
only get one X, any X chromosome linked gene a male inherits is expressed. If
female has only one X with trait, she is a carrier. Females usually get carrier
status from father’s X.
Ex: color-blindness – normal color vision is dominant, but if the
recessive gene is expressed the person is unable to see certain colors
properly. The gene is found on the X chromosome and is 10 times more
common in males.
Other Sex-linked Traits
Hemophilia: Blood clotting disorder, small cuts can be serious. Much more
common in males because it is on the X chromosome.
Duchenne Muscular Dystropy: 1/3000 males get it between ages 3-6.
Genetic disorder that causes muscle weakness because of a defective protein.
Looking for cure – insert a dominant allele into muscle cells
Human Genetic Disorders
Most genes are on autosome chromosomes (chromosomes 1-22)
NOT the sex-linked chromosomes
Genetic disorders carried on Autosomes:
- Albinism: recessive allele on chromosome 11
Not able to produce melanin – no pigment (color)
- Cystic Fibrosis: 1/2500 kids have it. Caused by defective protein in cell
membrane – results in thick mucus liquid clogs lungs, respiratory issues.
- Tay-Sachs Disease: common in Jewish families. Rapid breakdown of
nervous system.
- PKU – phenylketonuria. Causes mental retardation. Test and treatment
for PKU, special diet.
- Huntington Disease: Rare disorder carried by a dominant allele on
chromosome 4. No symptoms till age 30-40, start lose control of
muscles.
- Sickle-cell Anemia: blood disorder – RBCs shaped like sickle/crescent.
Does not carry as much oxygen in this shape. Painful, lack energy.
All of these genetic disorders are carried on autosomes (chromosomes 1-22,
not sex chromosomes): Albinism, Cystic Fibrosis, Tay Sachs, PKU, Huntington’s
Disease and Sickle Cell Anemia
Disorders due to abnormal pairing of chromosomes
Non-disjunction: chromosome pairs do not separate correctly, extra or
missing chromosomes
- Down Syndrome: Extra copy of chromosome 21 –
trisomy – 3 chromsomes. Causes mental retardation
- Klinefelter Syndrome: Males with extra X chromosome. XXY. Causes
mental retardation, sterility, small testes and breast development.
- Turner Syndrome: chromosomes don’t separate in meiosis. Sperm or
egg produced without sex chromosome. Zygote is XO.
Affects only females, sex organs do not develop properly.
Heart problems to minor cosmetic issues, small bone growth.
Chromosome Deletions: pieces of chromosome break off during meiosis.
Chromosome translocation: when pieces of chromosome break off and
reattach elsewhere. Affects vary.
Prenatal Diagnosis: tests before baby is born
- Can test for Down Syndrome, Tay-Sachs, Huntington Disease, etc
- Amniocentesis – takes small fluid from amniotic sac surrounding fetus.
Looks at cells in the fluid.
- Chorionic villus: Tissue of placenta is examined during 1st 10 wks
Turning off the X chromosome
- Women have XX, do we really need the genes on this extra X if males do
fine with just one X?
o Most female cells have a Barr body: a condensed turned off X
chromosome
o One of the X’s gets inactivated, unclear how, perhaps certain genes
on that X shut the others off
Gene Imprinting
Differences in trait based on which parent it comes from
Example: A defect on Chromosome 15:
- If the defect gene came from dad, child gets Angelman syndrome:
causes child to be short and obese
- If the defect gene came from mom, child gets Prader-Willi syndrome:
child is normal height, thin and hyperactive
Ethical Issues with Genetics:
Research into genes can help lead to cures, but on the other hand, who
should have access to that information?
You? Your spouse? Insurance Companies?
Human Genome Project
- A human cell contains 46 chromosomes that have 3 billion pairs of DNA
nucleotides. The Human Genome Project is a worldwide effort to identify the
complete nucleotide sequence in humans.
- This will help identify genes associated with genetic disorders
Manipulating DNA
Editing DNA – cut, transplant, rewrite, and/or splice together DNA
Cutting tool: biologists can cut DNA using restriction enzymes
These enzymes cut DNA at specific nucleotides
Separating tool: Electrophoresis Gel – DNA fragments placed in a gel and will
separate in gel based on size. Smaller pieces travel faster through gel.
DNA FINGERPRINTING
Splicing tool: Restriction enzymes cut DNA at certain places and leave some
bases exposed. Fragments of DNA can join together on these exposed ends.
Chapter 15: Genetic Engineering
Breeding Organisms
Selective Breeding: organisms with desired characteristics are selected to
produce a new generation.
Ex: Native Americans bred horses that were strong, fast (desired traits)
Also cats, dogs, and crop plants have been selectively bred
Hybridization: a cross between two different individuals
Ex: Labradoodle – one parent is Labrador other parent a Poodle.
Poodle: very intelligent, Labrador: playful, gentle
Inbreeding: breeding closely related individuals to maintain traits.
Risks – since most members of a breed are genetically similar, more chance of
bringing together 2 recessive alleles for a genetic defect. Some inbred dogs
end up being blind, have deformities.
Biotechnology: application of a technological process or invention to living
things. Selective breeding is a form of Biotechnology. Can use is to our
benefit by breeding desirable traits – stronger, healthier, more aesthetic, etc
- Increases variation, characteristics or options for living things
Polyploidy – 3 or more sets of chromosomes
- Bananas, oranges from polyploidy plants are bigger and better.
.
Recombinant DNA:
The process of combining DNA from two different sources. Taking DNA from
one organism and splicing it/combining it with another organism’s DNA
Splicing tool: Restriction enzymes cut DNA at certain places and leave some
bases exposed. Fragments of DNA can join together on these exposed ends.
Cell Transformation: putting recombinant DNA into a live cell. This will
change the cell’s original DNA by adding new DNA to it.
Plasmids: small circular pieces of DNA in bacteria and yeast. Scientists attach
pieces of DNA to plasmids to carry new DNA into cells.
Also, needle injected DNA into cells.
Engineering New Organisms
Genetic Engineering: cutting and splicing of genes and DNA from different
sources. Insert new genes into almost any organism, including humans.
Transgenic: organisms that have been transformed with genes from other
organisms.
Transgenic bacteria engineered to produce amounts insulin (a human
protein). The insulin is for diabetics who can’t produce enough insulin.
Transgenic cells used to make proteins for treating cancer & other disorders
Clone: producing a genetically identical organism from a single cell.
Genetic Engineering
Manipulating DNA to our benefit. Used to genetically engineer better crops in
agriculture, as well as in Human Gene Therapy to help improve health,
treating disease, and developing medicine.
Human Gene Therapy
- It is easier to transform human cells in a lab then in a living person
Cystic Fibrosis treatment: transformed viruses by injecting healthy alleles for
the Cystic Fibrosis gene into the viruses then sprayed them into patients’
nose/mouth. This helped symptoms, but once those cells with the good genes
died off the symptoms started to return.
Recent Human Genetics
Restriction Fragment Length Polymorphism (RFLP):
DNA is cut into small pieces, put through gel, and then a probe is used to
identify sequence of nucleotides. Different individuals have different RFLPs in
their DNA. Probes identify RFLPs and classify an individual’s DNA.
Can test for genetic diseases like: Huntington Disease, Sickle Cell Anemia,
Cystic Fibrosis, Tay Sachs, and other diseases using RFLPs to see which alleles
you have.
RFLPs also used in DNA Fingerprinting / Forensic Science
- Identifying RFLPs can distinguish DNA of one individual from another.
Blood Types
There are 3 alleles for blood Type: A, B, and O – written as IA, IB, I0
A and B are codominant, O is recessive.